/*
 * Copyright (c) 2007, 2021, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.sun.org.apache.xml.internal.dtm.ref;

import java.io.IOException;

import com.sun.org.apache.xml.internal.res.XMLErrorResources;
import com.sun.org.apache.xml.internal.res.XMLMessages;
import com.sun.org.apache.xml.internal.utils.ThreadControllerWrapper;

import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.DTDHandler;
import org.xml.sax.ErrorHandler;
import org.xml.sax.InputSource;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;
import org.xml.sax.SAXParseException;
import org.xml.sax.XMLReader;
import org.xml.sax.ext.LexicalHandler;

/**
 * <p>IncrementalSAXSource_Filter implements IncrementalSAXSource, using a
 * standard SAX2 event source as its input and parcelling out those
 * events gradually in reponse to deliverMoreNodes() requests.  Output from the
 * filter will be passed along to a SAX handler registered as our
 * listener, but those callbacks will pass through a counting stage
 * which periodically yields control back to the controller coroutine.
 * </p>
 *
 * <p>%REVIEW%: This filter is not currenly intended to be reusable
 * for parsing additional streams/documents. We may want to consider
 * making it resettable at some point in the future. But it's a
 * small object, so that'd be mostly a convenience issue; the cost
 * of allocating each time is trivial compared to the cost of processing
 * any nontrival stream.</p>
 *
 * <p>For a brief usage example, see the unit-test main() method.</p>
 *
 * <p>This is a simplification of the old CoroutineSAXParser, focusing
 * specifically on filtering. The resulting controller protocol is _far_
 * simpler and less error-prone; the only controller operation is deliverMoreNodes(),
 * and the only requirement is that deliverMoreNodes(false) be called if you want to
 * discard the rest of the stream and the previous deliverMoreNodes() didn't return
 * false.
 * <p>
 * This class is final and package private for security reasons. Please
 * see CR 6537912 for further details.
 */
final class IncrementalSAXSource_Filter
        implements IncrementalSAXSource, ContentHandler, DTDHandler, LexicalHandler, ErrorHandler, Runnable {
    boolean DEBUG = false; //Internal status report

    //
    // Data
    //
    private CoroutineManager fCoroutineManager = null;
    private int fControllerCoroutineID = -1;
    private int fSourceCoroutineID = -1;

    private ContentHandler clientContentHandler = null; // %REVIEW% support multiple?
    private LexicalHandler clientLexicalHandler = null; // %REVIEW% support multiple?
    private DTDHandler clientDTDHandler = null; // %REVIEW% support multiple?
    private ErrorHandler clientErrorHandler = null; // %REVIEW% support multiple?
    private int eventcounter;
    private int frequency = 5;

    // Flag indicating that no more events should be delivered -- either
    // because input stream ran to completion (endDocument), or because
    // the user requested an early stop via deliverMoreNodes(false).
    private boolean fNoMoreEvents = false;

    // Support for startParse()
    private XMLReader fXMLReader = null;
    private InputSource fXMLReaderInputSource = null;

    //
    // Constructors
    //

    public IncrementalSAXSource_Filter() {
        this.init(new CoroutineManager(), -1, -1);
    }

    /**
     * Create a IncrementalSAXSource_Filter which is not yet bound to a specific
     * SAX event source.
     */
    public IncrementalSAXSource_Filter(CoroutineManager co, int controllerCoroutineID) {
        this.init(co, controllerCoroutineID, -1);
    }

    //
    // Factories
    //
    static public IncrementalSAXSource createIncrementalSAXSource(CoroutineManager co, int controllerCoroutineID) {
        return new IncrementalSAXSource_Filter(co, controllerCoroutineID);
    }

    //
    // Public methods
    //

    public void init(CoroutineManager co, int controllerCoroutineID,
                     int sourceCoroutineID) {
        if (co == null)
            co = new CoroutineManager();
        fCoroutineManager = co;
        fControllerCoroutineID = co.co_joinCoroutineSet(controllerCoroutineID);
        fSourceCoroutineID = co.co_joinCoroutineSet(sourceCoroutineID);
        if (fControllerCoroutineID == -1 || fSourceCoroutineID == -1)
            throw new RuntimeException(XMLMessages.createXMLMessage(XMLErrorResources.ER_COJOINROUTINESET_FAILED, null)); //"co_joinCoroutineSet() failed");

        fNoMoreEvents = false;
        eventcounter = frequency;
    }

    /**
     * Bind our input streams to an XMLReader.
     * <p>
     * Just a convenience routine; obviously you can explicitly register
     * this as a listener with the same effect.
     */
    public void setXMLReader(XMLReader eventsource) {
        fXMLReader = eventsource;
        eventsource.setContentHandler(this);
        eventsource.setDTDHandler(this);
        eventsource.setErrorHandler(this); // to report fatal errors in filtering mode

        // Not supported by all SAX2 filters:
        try {
            eventsource.
                    setProperty("http://xml.org/sax/properties/lexical-handler",
                            this);
        } catch (SAXNotRecognizedException e) {
            // Nothing we can do about it
        } catch (SAXNotSupportedException e) {
            // Nothing we can do about it
        }

        // Should we also bind as other varieties of handler?
        // (DTDHandler and so on)
    }

    // Register a content handler for us to output to
    public void setContentHandler(ContentHandler handler) {
        clientContentHandler = handler;
    }

    // Register a DTD handler for us to output to
    public void setDTDHandler(DTDHandler handler) {
        clientDTDHandler = handler;
    }

    // Register a lexical handler for us to output to
    // Not all filters support this...
    // ??? Should we register directly on the filter?
    // NOTE NAME -- subclassing issue in the Xerces version
    public void setLexicalHandler(LexicalHandler handler) {
        clientLexicalHandler = handler;
    }

    // Register an error handler for us to output to
    // NOTE NAME -- subclassing issue in the Xerces version
    public void setErrHandler(ErrorHandler handler) {
        clientErrorHandler = handler;
    }

    // Set the number of events between resumes of our coroutine
    // Immediately resets number of events before _next_ resume as well.
    public void setReturnFrequency(int events) {
        if (events < 1) events = 1;
        frequency = eventcounter = events;
    }

    //
    // ContentHandler methods
    // These  pass the data to our client ContentHandler...
    // but they also count the number of events passing through,
    // and resume our coroutine each time that counter hits zero and
    // is reset.
    //
    // Note that for everything except endDocument and fatalError, we do the count-and-yield
    // BEFORE passing the call along. I'm hoping that this will encourage JIT
    // compilers to realize that these are tail-calls, reducing the expense of
    // the additional layer of data flow.
    //
    // %REVIEW% Glenn suggests that pausing after endElement, endDocument,
    // and characters may be sufficient. I actually may not want to
    // stop after characters, since in our application these wind up being
    // concatenated before they're processed... but that risks huge blocks of
    // text causing greater than usual readahead. (Unlikely? Consider the
    // possibility of a large base-64 block in a SOAP stream.)
    //
    public void characters(char[] ch, int start, int length)
            throws org.xml.sax.SAXException {
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.characters(ch, start, length);
    }

    public void endDocument()
            throws org.xml.sax.SAXException {
        // EXCEPTION: In this case we need to run the event BEFORE we yield.
        if (clientContentHandler != null)
            clientContentHandler.endDocument();

        eventcounter = 0;
        co_yield(false);
    }

    public void endElement(java.lang.String namespaceURI, java.lang.String localName,
                           java.lang.String qName)
            throws org.xml.sax.SAXException {
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.endElement(namespaceURI, localName, qName);
    }

    public void endPrefixMapping(java.lang.String prefix)
            throws org.xml.sax.SAXException {
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.endPrefixMapping(prefix);
    }

    public void ignorableWhitespace(char[] ch, int start, int length)
            throws org.xml.sax.SAXException {
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.ignorableWhitespace(ch, start, length);
    }

    public void processingInstruction(java.lang.String target, java.lang.String data)
            throws org.xml.sax.SAXException {
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.processingInstruction(target, data);
    }

    public void setDocumentLocator(Locator locator) {
        if (--eventcounter <= 0) {
            // This can cause a hang.  -sb
            // co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.setDocumentLocator(locator);
    }

    public void skippedEntity(java.lang.String name)
            throws org.xml.sax.SAXException {
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.skippedEntity(name);
    }

    public void startDocument()
            throws org.xml.sax.SAXException {
        co_entry_pause();

        // Otherwise, begin normal event delivery
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.startDocument();
    }

    public void startElement(java.lang.String namespaceURI, java.lang.String localName,
                             java.lang.String qName, Attributes atts)
            throws org.xml.sax.SAXException {
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.startElement(namespaceURI, localName, qName, atts);
    }

    public void startPrefixMapping(java.lang.String prefix, java.lang.String uri)
            throws org.xml.sax.SAXException {
        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
        if (clientContentHandler != null)
            clientContentHandler.startPrefixMapping(prefix, uri);
    }

    //
    // LexicalHandler support. Not all SAX2 filters support these events
    // but we may want to pass them through when they exist...
    //
    // %REVIEW% These do NOT currently affect the eventcounter; I'm asserting
    // that they're rare enough that it makes little or no sense to
    // pause after them. As such, it may make more sense for folks who
    // actually want to use them to register directly with the filter.
    // But I want 'em here for now, to remind us to recheck this assertion!
    //
    public void comment(char[] ch, int start, int length)
            throws org.xml.sax.SAXException {
        if (null != clientLexicalHandler)
            clientLexicalHandler.comment(ch, start, length);
    }

    public void endCDATA()
            throws org.xml.sax.SAXException {
        if (null != clientLexicalHandler)
            clientLexicalHandler.endCDATA();
    }

    public void endDTD()
            throws org.xml.sax.SAXException {
        if (null != clientLexicalHandler)
            clientLexicalHandler.endDTD();
    }

    public void endEntity(java.lang.String name)
            throws org.xml.sax.SAXException {
        if (null != clientLexicalHandler)
            clientLexicalHandler.endEntity(name);
    }

    public void startCDATA()
            throws org.xml.sax.SAXException {
        if (null != clientLexicalHandler)
            clientLexicalHandler.startCDATA();
    }

    public void startDTD(java.lang.String name, java.lang.String publicId,
                         java.lang.String systemId)
            throws org.xml.sax.SAXException {
        if (null != clientLexicalHandler)
            clientLexicalHandler.startDTD(name, publicId, systemId);
    }

    public void startEntity(java.lang.String name)
            throws org.xml.sax.SAXException {
        if (null != clientLexicalHandler)
            clientLexicalHandler.startEntity(name);
    }

    //
    // DTDHandler support.

    public void notationDecl(String a, String b, String c) throws SAXException {
        if (null != clientDTDHandler)
            clientDTDHandler.notationDecl(a, b, c);
    }

    public void unparsedEntityDecl(String a, String b, String c, String d) throws SAXException {
        if (null != clientDTDHandler)
            clientDTDHandler.unparsedEntityDecl(a, b, c, d);
    }

    //
    // ErrorHandler support.
    //
    // PROBLEM: Xerces is apparently _not_ calling the ErrorHandler for
    // exceptions thrown by the ContentHandler, which prevents us from
    // handling this properly when running in filtering mode with Xerces
    // as our event source.  It's unclear whether this is a Xerces bug
    // or a SAX design flaw.
    //
    // %REVIEW% Current solution: In filtering mode, it is REQUIRED that
    // event source make sure this method is invoked if the event stream
    // abends before endDocument is delivered. If that means explicitly calling
    // us in the exception handling code because it won't be delivered as part
    // of the normal SAX ErrorHandler stream, that's fine; Not Our Problem.
    //
    public void error(SAXParseException exception) throws SAXException {
        if (null != clientErrorHandler)
            clientErrorHandler.error(exception);
    }

    public void fatalError(SAXParseException exception) throws SAXException {
        // EXCEPTION: In this case we need to run the event BEFORE we yield --
        // just as with endDocument, this terminates the event stream.
        if (null != clientErrorHandler)
            clientErrorHandler.error(exception);

        eventcounter = 0;
        co_yield(false);

    }

    public void warning(SAXParseException exception) throws SAXException {
        if (null != clientErrorHandler)
            clientErrorHandler.error(exception);
    }


    //
    // coroutine support
    //

    public int getSourceCoroutineID() {
        return fSourceCoroutineID;
    }

    public int getControllerCoroutineID() {
        return fControllerCoroutineID;
    }

    /**
     * @return the CoroutineManager this CoroutineFilter object is bound to.
     * If you're using the do...() methods, applications should only
     * need to talk to the CoroutineManager once, to obtain the
     * application's Coroutine ID.
     */
    public CoroutineManager getCoroutineManager() {
        return fCoroutineManager;
    }

    /**
     * <p>In the SAX delegation code, I've inlined the count-down in
     * the hope of encouraging compilers to deliver better
     * performance. However, if we subclass (eg to directly connect the
     * output to a DTM builder), that would require calling super in
     * order to run that logic... which seems inelegant.  Hence this
     * routine for the convenience of subclasses: every [frequency]
     * invocations, issue a co_yield.</p>
     *
     * @param moreExepected Should always be true unless this is being called
     *                      at the end of endDocument() handling.
     */
    protected void count_and_yield(boolean moreExpected) throws SAXException {
        if (!moreExpected) eventcounter = 0;

        if (--eventcounter <= 0) {
            co_yield(true);
            eventcounter = frequency;
        }
    }

    /**
     * co_entry_pause is called in startDocument() before anything else
     * happens. It causes the filter to wait for a "go ahead" request
     * from the controller before delivering any events. Note that
     * the very first thing the controller tells us may be "I don't
     * need events after all"!
     */
    private void co_entry_pause() throws SAXException {
        if (fCoroutineManager == null) {
            // Nobody called init()? Do it now...
            init(null, -1, -1);
        }

        try {
            Object arg = fCoroutineManager.co_entry_pause(fSourceCoroutineID);
            if (arg == Boolean.FALSE)
                co_yield(false);
        } catch (NoSuchMethodException e) {
            // Coroutine system says we haven't registered. That's an
            // application coding error, and is unrecoverable.
            if (DEBUG) e.printStackTrace();
            throw new SAXException(e);
        }
    }

    /**
     * Co_Yield handles coroutine interactions while a parse is in progress.
     * <p>
     * When moreRemains==true, we are pausing after delivering events, to
     * ask if more are needed. We will resume the controller thread with
     * co_resume(Boolean.TRUE, ...)
     * When control is passed back it may indicate
     * Boolean.TRUE    indication to continue delivering events
     * Boolean.FALSE   indication to discontinue events and shut down.
     * <p>
     * When moreRemains==false, we shut down immediately without asking the
     * controller's permission. Normally this means end of document has been
     * reached.
     * <p>
     * Shutting down a IncrementalSAXSource_Filter requires terminating the incoming
     * SAX event stream. If we are in control of that stream (if it came
     * from an XMLReader passed to our startReader() method), we can do so
     * very quickly by throwing a reserved exception to it. If the stream is
     * coming from another source, we can't do that because its caller may
     * not be prepared for this "normal abnormal exit", and instead we put
     * ourselves in a "spin" mode where events are discarded.
     */
    private void co_yield(boolean moreRemains) throws SAXException {
        // Horrendous kluge to run filter to completion. See below.
        if (fNoMoreEvents)
            return;

        try // Coroutine manager might throw no-such.
        {
            Object arg = Boolean.FALSE;
            if (moreRemains) {
                // Yield control, resume parsing when done
                arg = fCoroutineManager.co_resume(Boolean.TRUE, fSourceCoroutineID,
                        fControllerCoroutineID);

            }

            // If we're at end of document or were told to stop early
            if (arg == Boolean.FALSE) {
                fNoMoreEvents = true;

                if (fXMLReader != null)    // Running under startParseThread()
                    throw new StopException(); // We'll co_exit from there.

                // Yield control. We do NOT expect anyone to ever ask us again.
                fCoroutineManager.co_exit_to(Boolean.FALSE, fSourceCoroutineID,
                        fControllerCoroutineID);
            }
        } catch (NoSuchMethodException e) {
            // Shouldn't happen unless we've miscoded our coroutine logic
            // "Shut down the garbage smashers on the detention level!"
            fNoMoreEvents = true;
            fCoroutineManager.co_exit(fSourceCoroutineID);
            throw new SAXException(e);
        }
    }

    //
    // Convenience: Run an XMLReader in a thread
    //

    /**
     * Launch a thread that will run an XMLReader's parse() operation within
     * a thread, feeding events to this IncrementalSAXSource_Filter. Mostly a convenience
     * routine, but has the advantage that -- since we invoked parse() --
     * we can halt parsing quickly via a StopException rather than waiting
     * for the SAX stream to end by itself.
     *
     * @throws SAXException is parse thread is already in progress
     *                      or parsing can not be started.
     */
    public void startParse(InputSource source) throws SAXException {
        if (fNoMoreEvents)
            throw new SAXException(XMLMessages.createXMLMessage(XMLErrorResources.ER_INCRSAXSRCFILTER_NOT_RESTARTABLE, null)); //"IncrmentalSAXSource_Filter not currently restartable.");
        if (fXMLReader == null)
            throw new SAXException(XMLMessages.createXMLMessage(XMLErrorResources.ER_XMLRDR_NOT_BEFORE_STARTPARSE, null)); //"XMLReader not before startParse request");

        fXMLReaderInputSource = source;

        // Xalan thread pooling...
        // com.sun.org.apache.xalan.internal.transformer.TransformerImpl.runTransformThread(this);
        ThreadControllerWrapper.runThread(this, -1);
    }

    /* Thread logic to support startParseThread()
     */
    public void run() {
        // Guard against direct invocation of start().
        if (fXMLReader == null) return;

        if (DEBUG) System.out.println("IncrementalSAXSource_Filter parse thread launched");

        // Initially assume we'll run successfully.
        Object arg = Boolean.FALSE;

        // For the duration of this operation, all coroutine handshaking
        // will occur in the co_yield method. That's the nice thing about
        // coroutines; they give us a way to hand off control from the
        // middle of a synchronous method.
        try {
            fXMLReader.parse(fXMLReaderInputSource);
        } catch (IOException ex) {
            arg = ex;
        } catch (StopException ex) {
            // Expected and harmless
            if (DEBUG) System.out.println("Active IncrementalSAXSource_Filter normal stop exception");
        } catch (SAXException ex) {
            Exception inner = ex.getException();
            if (inner instanceof StopException) {
                // Expected and harmless
                if (DEBUG) System.out.println("Active IncrementalSAXSource_Filter normal stop exception");
            } else {
                // Unexpected malfunction
                if (DEBUG) {
                    System.out.println("Active IncrementalSAXSource_Filter UNEXPECTED SAX exception: " + inner);
                    inner.printStackTrace();
                }
                arg = ex;
            }
        } // end parse

        // Mark as no longer running in thread.
        fXMLReader = null;

        try {
            // Mark as done and yield control to the controller coroutine
            fNoMoreEvents = true;
            fCoroutineManager.co_exit_to(arg, fSourceCoroutineID,
                    fControllerCoroutineID);
        } catch (java.lang.NoSuchMethodException e) {
            // Shouldn't happen unless we've miscoded our coroutine logic
            // "CPO, shut down the garbage smashers on the detention level!"
            e.printStackTrace(System.err);
            fCoroutineManager.co_exit(fSourceCoroutineID);
        }
    }

    /**
     * Used to quickly terminate parse when running under a
     * startParse() thread. Only its type is important.
     */
    class StopException extends RuntimeException {
        static final long serialVersionUID = -1129245796185754956L;
    }

    /**
     * deliverMoreNodes() is a simple API which tells the coroutine
     * parser that we need more nodes.  This is intended to be called
     * from one of our partner routines, and serves to encapsulate the
     * details of how incremental parsing has been achieved.
     *
     * @param parsemore If true, tells the incremental filter to generate
     *                  another chunk of output. If false, tells the filter that we're
     *                  satisfied and it can terminate parsing of this document.
     * @return Boolean.TRUE if there may be more events available by invoking
     * deliverMoreNodes() again. Boolean.FALSE if parsing has run to completion (or been
     * terminated by deliverMoreNodes(false). Or an exception object if something
     * malfunctioned. %REVIEW% We _could_ actually throw the exception, but
     * that would require runinng deliverMoreNodes() in a try/catch... and for many
     * applications, exception will be simply be treated as "not TRUE" in
     * any case.
     */
    public Object deliverMoreNodes(boolean parsemore) {
        // If parsing is already done, we can immediately say so
        if (fNoMoreEvents)
            return Boolean.FALSE;

        try {
            Object result =
                    fCoroutineManager.co_resume(parsemore ? Boolean.TRUE : Boolean.FALSE,
                            fControllerCoroutineID, fSourceCoroutineID);
            if (result == Boolean.FALSE)
                fCoroutineManager.co_exit(fControllerCoroutineID);

            return result;
        }

        // SHOULD NEVER OCCUR, since the coroutine number and coroutine manager
        // are those previously established for this IncrementalSAXSource_Filter...
        // So I'm just going to return it as a parsing exception, for now.
        catch (NoSuchMethodException e) {
            return e;
        }
    }


    //================================================================
    /** Simple unit test. Attempt coroutine parsing of document indicated
     * by first argument (as a URI), report progress.
     */
    /*
  public static void _main(String args[])
  {
    System.out.println("Starting...");

    org.xml.sax.XMLReader theSAXParser=
      new com.sun.org.apache.xerces.internal.parsers.SAXParser();


    for(int arg=0;arg<args.length;++arg)
    {
      // The filter is not currently designed to be restartable
      // after a parse has ended. Generate a new one each time.
      IncrementalSAXSource_Filter filter=
        new IncrementalSAXSource_Filter();
      // Use a serializer as our sample output
      com.sun.org.apache.xml.internal.serialize.XMLSerializer trace;
      trace=new com.sun.org.apache.xml.internal.serialize.XMLSerializer(System.out,null);
      filter.setContentHandler(trace);
      filter.setLexicalHandler(trace);

      try
      {
        InputSource source = new InputSource(args[arg]);
        Object result=null;
        boolean more=true;

        // init not issued; we _should_ automagically Do The Right Thing

        // Bind parser, kick off parsing in a thread
        filter.setXMLReader(theSAXParser);
        filter.startParse(source);

        for(result = filter.deliverMoreNodes(more);
            (result instanceof Boolean && ((Boolean)result)==Boolean.TRUE);
            result = filter.deliverMoreNodes(more))
        {
          System.out.println("\nSome parsing successful, trying more.\n");

          // Special test: Terminate parsing early.
          if(arg+1<args.length && "!".equals(args[arg+1]))
          {
            ++arg;
            more=false;
          }

        }

        if (result instanceof Boolean && ((Boolean)result)==Boolean.FALSE)
        {
          System.out.println("\nFilter ended (EOF or on request).\n");
        }
        else if (result == null) {
          System.out.println("\nUNEXPECTED: Filter says shut down prematurely.\n");
        }
        else if (result instanceof Exception) {
          System.out.println("\nFilter threw exception:");
          ((Exception)result).printStackTrace();
        }

      }
      catch(SAXException e)
      {
        e.printStackTrace();
      }
    } // end for
  }
    */
} // class IncrementalSAXSource_Filter
